1. Field of the Invention
The invention relates generally to photography, and particularly to a film cassette with a magnetic film leader.
2. Description of the Prior Art
Generally speaking, commercially available 35 mm film cassettes such as manufactured by Eastman Kodak Co. and Fuji Photo Co., Ltd. comprise a hollow cylindrical shell having an integral throat or lipped portion which extends tangentially from the shell. A film spool on which the filmstrip is wound is freely rotatable within the cassette shell. The filmstrip has a leading section, commonly referred to as a "film leader", which protrudes from a light-trapped slit in the throat portion to the outside of the cassette shell. Typically, the protruding leader extends 2-3 inches in length.
In conventional 35 mm film cassettes, one end of the film spool on which the filmstrip is wound has a short axial extension which projects from the cassette shell, enabling the spool to be turned by hand. If the spool is manually rotated initially in an unwinding direction, the film convolutions inside the cassette shell will tend to expand radially since the inner end of the filmstrip is attached to the spool, and the film leader protruding from the slit will remain stationary. The film convolutions can expand radially until a non-slipping relation is established between the outermost convolution and the inner curved wall of the cassette shell. Once this non-slipping relation exists, there is a binding effect between the outermost convolution and the shell which prevents further rotation of the spool in the unwinding direction. Consequently, rotation of the spool in the unwinding direction cannot serve to advance the filmstrip out of the shell, and it is necessary in the typical 35 mm camera to engage the protruding leader to pull the filmstrip out of the shell. If the spool is manually rotated initially in a winding direction, it will draw the protruding leader into the shell. Thus, the film leader will not be able to be engaged to pull the filmstrip out of the shell.
A 35 mm film cassette has been proposed which, unlike conventional film cassettes, includes a film leader that does not extend outside the cassette shell. The film leader, instead, is located entirely within the cassette shell. Specifically, in U.S. Pat. No. 4,423,943, granted Jan. 3, 1984, there is disclosed a film cassette wherein the outermost convolution of the film roll wound on the film spool is radially constrained by respective circumferential lips of two axially spaced flanges of the spool to prevent the outermost convolution from contacting an inner wall of the cassette shell. The trailing end of the filmstrip is secured to the film spool, and the leading end of the filmstrip is reduced in width to allow it to protrude from between the circumferential lips and rest against the shell wall. During unwinding rotation of the film spool, the leading end of the filmstrip is advanced to and through a film passageway opening in order to exit the cassette shell. Thus, all that is needed to advance the film leader to the outside of the cassette shell is to rotate the film spool in an unwinding direction
While the film cassette disclosed in U.S. Pat. No. 4,423,943 includes a non-protruding film leader which is automatically advanced to the outside of the cassette shell when the film spool is rotated in the undwinding direction, the film cassette is intended to be loaded in a camera only after the film leader is advanced to protrude from the cassette shell. In the patent, it is suggested that one manually rotate the film spool relative to the cassette shell until the leader can be manually grasped and attached to a film advancing device in the camera.